<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>hover</title>
  <style>
    #test{width: 160px;background: #000;color: #fff;
      border-bottom: 3px solid hotpink;
    }
    #test p{font-size: 32px;color: hotpink;}
    .changed{height: 320px;background: gray;}

    #test:hover p{font-size: 16px; color: aqua;}
    #test:hover+.changed{background: purple;color: gold;}
  </style>
</head>
<body>
  <div id="test">
    HELLO WORLD!
    <p>HOVER</p>
  </div>
  <div class="changed">HAHAHA</div>
</body>
</html>